The invention relates to electronic semiconductor devices, and, more particularly, to gate structures and fabrication methods for integrated circuits.
The trend in semiconductor integrated circuits to higher device densities by down-scaling structure sizes and operating voltages has led to silicon field effect (MOS) transistor gate dielectrics, typically made of silicon dioxide, to approach thicknesses on the order of 1-2 nm to maintain the capacitive coupling of the gate to the channel. However, such thin oxides present leakage current problems due to carrier tunneling through the oxide. Consequently, alternative gate dielectrics with greater dielectric constants to permit greater physical thicknesses have been proposed. Indeed, Ta2O5, (Ba, Sr)TiO3, and other high dielectric constant materials have been suggested, but such materials have poor interface stability with silicon.
Wilk and Wallace, Electrical Properties of Hafnium Silicate Gate Dielectrics Deposited Directly on Silicon, 74 Appl. Phys. Lett. 2854 (1999) disclose measurements on capacitors with a hafnium silicate dielectric formed by sputtering deposition (at a pressure of 5×10−6 mTorr and substrate temperature of 500° C.) of a 5 nm thick Hf6Si29O65 (Hf0.18SiO0.89O2) layer directly onto silicon together with a gold top electrode deposition on the silicate dielectric. Such capacitors showed low leakage current, thermal stability, an effective dielectric constant of about 11, and a breakdown field of 10 MV/cm.
However, with high volume production of silicon integrated circuits such high-k gate dielectrics have problems such as control of leakage currents.